In their paper, Morris et al. investigate whether schizophrenia is
associated with altered neural responses in the ventral striatum to rewards,
surprise, or prediction errors. Sixteen patients and 16 matched, healthy controls
performed a modified reward task. This task contains standard reward trials
(a monetary reward after a correct or fast response) and omission trials (no
reward). These trials are standard in that participants can more or less
predict (expect) if they will receive a reward or not. Interestingly—and
this is what makes the paradigm stand out from the more basic reward tasks—a small number of trials participants unexpectedly receive or fail to
receive a reward. In this way, the impact of prediction error and surprise
could be disentangled from standard reward processing.

While the above approach is interesting, some weaknesses should be noted
that prevent the results from being fully convincing. First, the statistical
analysis resulted in clusters of above 1,000 voxels, suggesting that the
threshold was too low. Second, the definition of the ventral striatum
including a large dorsal region is questionable. Third, the patients in the
study were all on medication. This makes it difficult to interpret the
results. Not only are there known effects of medication at a neuronal level
(dopamine suppression in the primary region of interest), but also possible
cardiovascular changes. Finally, the study would benefit greatly from a
(far) larger sample of participants, which would allow between-subject
testing based on genes or even symptoms. In this way, the vast heterogeneity
within the patient population would be better addressed, which is of crucial
importance for increasing our understanding of how the brain is affected by
schizophrenia.